Message-ID: <CAHC9VhSUnq-+bMYCBvc4yyw9bkMNTChdn1m2b4Vn2i0e54AxxQ@mail.gmail.com>
Date:   Wed, 25 Aug 2021 14:31:10 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     casey@...aufler-ca.com
Cc:     davem@...emloft.net, kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        syzbot <syzbot+3f91de0b813cc3d19a80@...kaller.appspotmail.com>
Subject: Re: [syzbot] KASAN: use-after-free Read in netlbl_catmap_walk

On Wed, Aug 25, 2021 at 1:21 PM syzbot
<syzbot+3f91de0b813cc3d19a80@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    6e764bcd1cf7 Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=124e77c5300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2fd902af77ff1e56
> dashboard link: https://syzkaller.appspot.com/bug?extid=3f91de0b813cc3d19a80
> compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13f72f16300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=133e338d300000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3f91de0b813cc3d19a80@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in _netlbl_catmap_getnode net/netlabel/netlabel_kapi.c:564 [inline]
> BUG: KASAN: use-after-free in netlbl_catmap_walk+0x28b/0x2e0 net/netlabel/netlabel_kapi.c:615
> Read of size 4 at addr ffff8880161c9800 by task syz-executor742/8768
>
> CPU: 0 PID: 8768 Comm: syz-executor742 Not tainted 5.14.0-rc7-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1ae/0x29f lib/dump_stack.c:105
>  print_address_description+0x66/0x3b0 mm/kasan/report.c:233
>  __kasan_report mm/kasan/report.c:419 [inline]
>  kasan_report+0x163/0x210 mm/kasan/report.c:436
>  _netlbl_catmap_getnode net/netlabel/netlabel_kapi.c:564 [inline]
>  netlbl_catmap_walk+0x28b/0x2e0 net/netlabel/netlabel_kapi.c:615
>  cipso_seq_show+0x15f/0x280 security/smack/smackfs.c:789
>  traverse+0x1dc/0x530 fs/seq_file.c:111
>  seq_lseek+0x12b/0x240 fs/seq_file.c:323
>  vfs_llseek fs/read_write.c:300 [inline]
>  ksys_lseek fs/read_write.c:313 [inline]
>  __do_sys_lseek fs/read_write.c:324 [inline]
>  __se_sys_lseek fs/read_write.c:322 [inline]
>  __x64_sys_lseek+0x15b/0x1e0 fs/read_write.c:322
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x445889
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f9a9cff0318 EFLAGS: 00000246 ORIG_RAX: 0000000000000008
> RAX: ffffffffffffffda RBX: 00000000004ca408 RCX: 0000000000445889
> RDX: 0000000000000000 RSI: 0000000100000001 RDI: 0000000000000003
> RBP: 00000000004ca400 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004ca40c
> R13: 00007ffead4e31bf R14: 00007f9a9cff0400 R15: 0000000000022000
>
> Allocated by task 8768:
>  kasan_save_stack mm/kasan/common.c:38 [inline]
>  kasan_set_track mm/kasan/common.c:46 [inline]
>  set_alloc_info mm/kasan/common.c:434 [inline]
>  ____kasan_kmalloc+0xcd/0x100 mm/kasan/common.c:513
>  kasan_kmalloc include/linux/kasan.h:264 [inline]
>  kmem_cache_alloc_trace+0x96/0x340 mm/slub.c:2986
>  kmalloc include/linux/slab.h:591 [inline]
>  kzalloc include/linux/slab.h:721 [inline]
>  netlbl_catmap_alloc include/net/netlabel.h:317 [inline]
>  _netlbl_catmap_getnode net/netlabel/netlabel_kapi.c:582 [inline]
>  netlbl_catmap_setbit+0x1cb/0x3f0 net/netlabel/netlabel_kapi.c:782
>  smk_netlbl_mls+0x103/0x5e0 security/smack/smack_access.c:505
>  smk_set_cipso+0x621/0x810 security/smack/smackfs.c:921
>  vfs_write+0x289/0xc90 fs/read_write.c:603
>  ksys_write+0x171/0x2a0 fs/read_write.c:658
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Freed by task 8769:
>  kasan_save_stack mm/kasan/common.c:38 [inline]
>  kasan_set_track+0x3d/0x70 mm/kasan/common.c:46
>  kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
>  ____kasan_slab_free+0x10d/0x150 mm/kasan/common.c:366
>  kasan_slab_free include/linux/kasan.h:230 [inline]
>  slab_free_hook mm/slub.c:1628 [inline]
>  slab_free_freelist_hook+0x1e8/0x2a0 mm/slub.c:1653
>  slab_free mm/slub.c:3213 [inline]
>  kfree+0xcf/0x2e0 mm/slub.c:4267
>  netlbl_catmap_free include/net/netlabel.h:335 [inline]
>  smk_set_cipso+0x682/0x810 security/smack/smackfs.c:923
>  vfs_write+0x289/0xc90 fs/read_write.c:603
>  ksys_write+0x171/0x2a0 fs/read_write.c:658
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The buggy address belongs to the object at ffff8880161c9800
>  which belongs to the cache kmalloc-64 of size 64
> The buggy address is located 0 bytes inside of
>  64-byte region [ffff8880161c9800, ffff8880161c9840)
> The buggy address belongs to the page:
> page:ffffea0000587240 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x161c9
> flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000200 0000000000000000 0000000b00000001 ffff888011041640
> raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 6484, ts 27339779214, free_ts 27310944203
>  prep_new_page mm/page_alloc.c:2436 [inline]
>  get_page_from_freelist+0x779/0xa30 mm/page_alloc.c:4168
>  __alloc_pages+0x26c/0x5f0 mm/page_alloc.c:5390
>  alloc_slab_page mm/slub.c:1691 [inline]
>  allocate_slab+0xf1/0x540 mm/slub.c:1831
>  new_slab mm/slub.c:1894 [inline]
>  new_slab_objects mm/slub.c:2640 [inline]
>  ___slab_alloc+0x1cf/0x350 mm/slub.c:2803
>  __slab_alloc mm/slub.c:2843 [inline]
>  slab_alloc_node mm/slub.c:2925 [inline]
>  __kmalloc_node+0x310/0x430 mm/slub.c:4159
>  kmalloc_node include/linux/slab.h:614 [inline]
>  kvmalloc_node+0x81/0xf0 mm/util.c:587
>  kvmalloc include/linux/mm.h:806 [inline]
>  simple_xattr_alloc+0x3f/0xa0 fs/xattr.c:951
>  shmem_initxattrs+0x91/0x1e0 mm/shmem.c:3142
>  security_inode_init_security+0x37a/0x3c0 security/security.c:1099
>  shmem_mknod+0xb0/0x1b0 mm/shmem.c:2822
>  lookup_open fs/namei.c:3228 [inline]
>  open_last_lookups fs/namei.c:3298 [inline]
>  path_openat+0x13b7/0x36b0 fs/namei.c:3504
>  do_filp_open+0x253/0x4d0 fs/namei.c:3534
>  do_sys_openat2+0x124/0x460 fs/open.c:1204
>  do_sys_open fs/open.c:1220 [inline]
>  __do_sys_open fs/open.c:1228 [inline]
>  __se_sys_open fs/open.c:1224 [inline]
>  __x64_sys_open+0x221/0x270 fs/open.c:1224
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> page last free stack trace:
>  reset_page_owner include/linux/page_owner.h:24 [inline]
>  free_pages_prepare mm/page_alloc.c:1346 [inline]
>  free_pcp_prepare+0xc29/0xd20 mm/page_alloc.c:1397
>  free_unref_page_prepare mm/page_alloc.c:3332 [inline]
>  free_unref_page+0x7e/0x550 mm/page_alloc.c:3411
>  __vunmap+0x926/0xa70 mm/vmalloc.c:2587
>  free_work+0x66/0x90 mm/vmalloc.c:82
>  process_one_work+0x833/0x10c0 kernel/workqueue.c:2276
>  worker_thread+0xac1/0x1320 kernel/workqueue.c:2422
>  kthread+0x453/0x480 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>
> Memory state around the buggy address:
>  ffff8880161c9700: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>  ffff8880161c9780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> >ffff8880161c9800: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>                    ^
>  ffff8880161c9880: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8880161c9900: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches

Adding Casey to the To/CC line as I think this issue lies with Smack
and not NetLabel, although if someone believes otherwise please let me
know.

It looks like the problem is near the bottom of smk_set_cipso(), right
after smk_netlbl_mls() successfully creates the netlabel category
bitmap and attempts to free any old existing category bitmaps before
assigning the new value.  As I see it the problem is that the
smack_known pointer, @skp, which is host to the bitmap is located from
a RCU protected list meaning that it is possible for other tasks to be
accessing the category bitmap while it is being freed, or directly
afterwards given they may still be pointing at the old/freed data.

Casey obviously knows Smack much better than I do so I'll refrain from
going to far with a solution here in the likelihood that I'm off the
mark, but I suspect the right solution here would be to either
duplicate and replace the entry in the smack_known list using the
normal RCU list manipulation approach (easiest?), manage the
smack_known->smk_netlabel field as it's own RCU protected pointer
(less easy?), or something else entirely (wildcard!).  I'm not sure
this is a problem we can, or want to, solve at the NetLabel layer.

-- 
paul moore
www.paul-moore.com

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